Calculation method, calculation program and calculation system for information supporting arthroplasty

ABSTRACT

The present invention provides an arthroplasty supporting information calculation method for supporting diagnoses of a patient with knee disordered and total joint replacement to a total knee component, and an arthroplasty supporting information calculation program, and an arthroplasty supporting information calculation system. In an arthroplasty supporting terminal of the present invention, photographed X-ray images are acquired using X-ray irradiation mechanisms and a dedicated cassette base, Approximate three-dimensional data of a patient&#39;s bones is then created by transforming a display image of three-dimensional data of CT of the patient and/or sample bones to match the X-ray image in which the patient&#39;s bones are photographed. Three-dimensional coordinate values are then determined for this approximate three-dimensional data of the patient&#39;s bones. From these three-dimensional coordinate values, parameters are determined for evaluating positional relationships between at least two bones. The position of the display image of the three-dimensional data of a total knee component is then adjusted to match the display image of the approximate three-dimensional data of the patient&#39;s bones based on the three-dimensional coordinate values. The position of the total knee component is then calculated as anatomical coordinate values that represent the positions of at least two bones.

BACKGROUND OF T INVENTION

1. Field of the Invention

The present invention relates to an arthroplasty supporting informationcalculation method for calculating information that supports diagnosesof a patient with knee disordered and total joint replacement, and to anarthroplasty supporting information calculation program and arthroplastysupporting information calculation system.

2. Description of Related Art

Conventionally, in a diagnosis of knee joint ailment, the patient isplaced in a standing position and X-ray photography is performed fromtwo directions (i.e., from the front and side) on the lower limbs(centering on the knee joint and including the femur, the tibia, and thefibula). A doctor then makes a diagnosis by looking at these X-rayphotographs.

In the case of a patient with a severe knee joint disorders, a totaljoint replacement is performed. In this case, it is necessary to selecta total knee component that has a configuration and size that matchesthe knee joint of the patient and to determine the position of the totalknee component. Currently, the total knee component is selected and theposition thereof is determined by superimposing X-ray photographs ofknee joint taken from two directions at an equivalent magnification on asheet on which are printed projected configurations taken from twodirections of the total knee component.

However, in the above described conventional diagnosis method, becausethe alignment of the lower limbs (i.e., the positional relationshipbetween the femur and the tibia) of the patient which is intrinsicallythree-dimensional is determined based on X-ray photographs taken fromtwo dimensions which are two-dimensional images, a great deal ofreliance is often placed on the experience and intuition of the doctorand it is easy for discrepancies to occur in the diagnosis.

Moreover, in a total knee component as well, when selecting the totalknee component having a configuration and size to match the knee jointof the patient and when determining the position thereof, becausethree-dimensional confirmation is not possible a great deal of relianceis often placed on the experience and intuition of the doctor.Furthermore, it is difficult to accurately reproduce the position of thetotal knee component in an operation.

The present invention was conceived in view of the above circumstances,and is an object thereof to provide an arthroplasty supportinginformation calculation process for calculating information thatsupports diagnoses of the joint, selections of total knee component, anddeterminations of positions, which have hitherto depended a great dealon the experience of a doctor, and to an arthroplasty supportinginformation calculation program and arthroplasty supporting informationcalculation system.

SUMMARY OF THE INVENTION

In order to solve the above problems, the arthroplasty supportinginformation calculation method according to the first aspect of thepresent invention is an arthroplasty supporting information calculationmethod for calculating information that supports a diagnosis of apatient with knee disordered and total joint replacement to a total kneecomponent, comprising position coordinates acquisition processing (forexample, step S1 to S15 of the embodiment) in which a configuration of adisplay image of three-dimensional data of a sample bone is transformedso as to match an X-ray image obtained by photographing bones of thepatient so as to create three-dimensional data that is approximate tothe bones of the patient (for example, the three-dimensional data thatapproximates the bones of the patient in the embodiment describedbelow—hereinafter abbreviated to “approximate three-dimensional data”),and, in addition, in which three-dimensional coordinate values in realspace are determined for the approximate three-dimensional data; andevaluation parameter calculation processing (for example, step S16 ofthe embodiment) in which positional relationships of at least two bonesare evaluated from the approximate three-dimensional data and from thethree-dimensional coordinate values.

In this arthroplasty supporting information calculation method, in theposition coordinates acquisition processing, it is possible to easilyform bones, whose characteristics are different in each individualpatient, into a model using approximate three-dimensional data obtainedby transforming a configuration of a display image of three-dimensionaldata of sample bones so as to match the bones of the patient.Furthermore, in the evaluation parameter calculation processing, usingthree-dimensional coordinate values that are obtained from thisapproximate three-dimensional data, it is possible for each individualto accurately determine evaluation parameters that are used to evaluatepositional relationships in bones that require the total knee component.

Accordingly, diagnoses of joints of patients and operations to replacethe total knee component, which have conventionally relied a great dealon the experience and intuition of the doctor, can be performed basednot on determinations made using two-dimensional images, but on specificevaluation parameters determined from three-dimensional coordinatevalues. As a result, accurate diagnosis results or operation resultsthat do not rely on the experience and intuition of the doctor can beobtained.

The arthroplasty supporting information calculation method according tothe second aspect of the present invention is an arthroplasty supportinginformation calculation method for calculating information that supportsa diagnosis of a patient with knee disordered and total jointreplacement to a total knee component, comprising; position coordinatesacquisition processing (for example, step S1 to S15 of the embodiment)in which a configuration of a display image of three-dimensional data ofa sample bone is transformed so as to match an X-ray image obtained byphotographing bones of the patient so as to create the approximatethree-dimensional data (for example, the three-dimensional data thatapproximates the bones of the patient in the embodiment), and, inaddition, in which three-dimensional coordinate values in real space aredetermined for the approximate three-dimensional data; and total kneecomponent position calculation processing (for example, steps S17 to S19of the embodiments) in which a configuration and size of the total kneecomponent is selected for the display image of the approximatethree-dimensional data, and, as a result of a position of the displayimage of the three-dimensional data of the total knee component beingadjusted, a position for the total knee component is calculated ascoordinate values of anatomical coordinates of a bone where the totalknee component is to be placed.

In this arthroplasty supporting information calculation method, in theposition coordinates acquisition processing, bones, whosecharacteristics are different in each individual patient, are easilyformed into a model using approximate three-dimensional data obtained bytransforming a configuration of a display image of three-dimensionaldata of sample bones so as to match the bones of the patient, andthree-dimensional coordinate values obtained from this approximatethree-dimensional data are calculated. Furthermore, in the total kneecomponent position calculation processing, by adjusting the position ofa display image of the three-dimensional data of the total kneecomponent so that it matches a display image of the approximatethree-dimensional data based on the three-dimensional coordinate values,it is possible to calculate the position of the total knee component inanatomical coordinates that are set from these three-dimensionalcoordinate values.

Accordingly, it is possible to acquire the position of the total kneecomponent as specific anatomical coordinate numerical values. As aresult, it is possible to solve conventional problems such as a thatfact that great deal depends on the experience of the doctor, and thefact that it is difficult to accurately use or reproduce in thearthroplasty when the position of the total knee component once this hasbeen decided, and it is possible to increase stability in the result ofthe arthroplasty, improve safety, and improve reproducibility.

In the arthroplasty supporting information calculation method accordingto the third aspect of the present invention, in the above describedarthroplasty supporting information calculation method, the positioncoordinates acquisition processing derives a projection matrix thatrepresents a projection relationship between real space andtwo-dimensional planes of projection coming from two directions fromthree-dimensional coordinate values of a group of steel balls (forexample, the steel balls 6 b of the embodiment) whose three-dimensionalcoordinate values in real space are known and two-dimensional coordinatevalues of the group of steel balls that appears in X-ray images that areobtained by photographing the bones of the patient from two directions,and, using this projection matrix, determines three-dimensionalcoordinate values of the approximate three-dimensional data.

As a result, in the position coordinates acquisition processing, thebones of a patient are recognized three-dimensionally usingthree-dimensional coordinate values in real space of the group of steelballs and two-dimensional coordinate values taken from two directions ofthe group of steel balls, and the three-dimensional coordinate values ofthe bones of the patient can be accurately determined. Accordingly,provided they have X-ray images taken from two directions in whichappear a group of steel balls whose three-dimensional coordinate valuesare known, and by creating approximate three-dimensional data bytransforming the configuration of the display image of three-dimensionaldata of sample bones so that it matches X-ray images in which bones ofthe patient are photographed, all of the doctors that are involved in anoperation can easily acquire bone position information as accuratethree-dimensional coordinate values.

In the arthroplasty supporting information calculation method accordingto the fourth aspect of the present invention, in the arthroplastysupporting information calculation method according to the third aspect,the arthroplasty supporting information calculation method includesreference point acquisition processing in which points that showcharacteristics of bones that can be observed from both of twodirections are plotted on two-dimensional images that are taken from thetwo directions in which are displayed bones of the patient or bones thatapproximate a bone configuration of the patient, and reference pointsthat show characteristics and structures of the bones are determinedfrom the plotted points that show the characteristics of the bones, andthe position coordinate acquisition processing determinesthree-dimensional coordinate values of the approximate three-dimensionaldata by calculating three-dimensional coordinate values in real spacefrom the reference points using the projection matrix.

In this arthroplasty supporting information calculation method, usingthe bone reference point acquisition processing, the positions of bones,whose configuration is different for each individual patient, areextracted as position information of reference points of bones that havebeen formed into models using points that show the characteristicsthereof. As a result, in the position coordinate acquisition processing,without using position information on all portions of the bones, it ispossible to easily determine three-dimensional coordinate values ofbones of the patient using a small amount of calculation processing froma projection matrix derived using position information on the referencepoints and X-ray images photographed from two directions.

Accordingly, even if the bones have a complex configuration, providedthat the characteristic points of the bones can be determined, all ofthe doctors involved in the arthroplasty axe able to acquire positioninformation on the bones as three dimensional coordinate values in ashort time.

In the arthroplasty supporting information calculation method accordingto the fifth aspect of the present invention, in the arthroplastysupporting information calculation method according to the fourthaspect, the reference point acquisition processing determines thereference points by approximating a surface configuration of a bone fromplotted points that show characteristics of the bone.

In this arthroplasty supporting information calculation method, bydetermining reference points after replacing a configuration that showsplotted bone characteristics with a simple diagram, it is possible toperform the bone reference point acquisition processing with an evensmaller amount of calculation processing without any reduction inaccuracy. Accordingly, during the drafting of an operation plan, it ispossible to allocate time with priority given to other tasks (i.e., totasks such as determining three-dimensional coordinate values of theapproximate three-dimensional data, and calculating a position of thetotal knee component based on the determined three-dimensionalcoordinate values).

In the arthroplasty supporting information calculation method accordingto the sixth aspect of the present invention, in the arthroplastysupporting information calculation method according to the first aspect,there is included reference point acquisition processing in which pointsthat show characteristics of bones that can be observed from both of twodirections are plotted on two-dimensional images that are taken from thetwo directions in which are displayed bones of the patient or bones thatapproximate a configuration of bones of the patient, and referencepoints that show structures of the bones are determined as a result of asurface configuration of the bones being approximated from the plottedpoints that show the characteristics of the bones, and the evaluationparameter calculation processing determines the parameters using thesereference points.

As a result, in the evaluation parameter calculation processing, withoutusing three-dimensional coordinate values of all portions of the bones,it is possible to easily calculate evaluation parameters by a smallamount of calculation processing from the three-dimensional coordinatevalues of reference points determined in the reference point acquisitionprocessing. As a result, an effect corresponding to that of thearthroplasty supporting information calculation method according to thefourth aspect of the present invention can be obtained.

The arthroplasty supporting information calculation program according tothe seventh aspect of the present invention is an arthroplastysupporting information calculation program for calculating informationthat supports a diagnosis of a patient with knee disordered and totaljoint replacement to a total knee component, that executes on acomputer: position coordinates acquisition processing in which aconfiguration of a display image of three-dimensional data of a samplebone is transformed so as to match an X-ray image obtained byphotographing bones of the patient so as to create the approximatethree-dimensional data, and, in addition, in which three-dimensionalcoordinate values in real space are determined for the approximatethree-dimensional data; and evaluation parameter calculation processingin which positional relationships of at least two bones are evaluatedfrom the approximate three-dimensional data and from thethree-dimensional coordinate values of the bones of the patient.

The arthroplasty supporting information calculation program according tothe eighth aspect of the present invention is an arthroplasty supportinginformation calculation program for calculating information thatsupports a diagnosis of a patient with knee disordered and total jointreplacement to a total knee component, that executes on a computer:position coordinates acquisition processing in which a configuration ofa display image of three-dimensional data of a sample bone istransformed so as to match an X-ray image obtained by photographingbones of the patient so as to create the approximate three-dimensionaldata, and, in addition, in which three-dimensional coordinate values inreal space are determined for the approximate three-dimensional data;and total knee component position calculation processing in which aconfiguration and size of the total knee component is selected for thedisplay image of the approximate three-dimensional data, and, as aresult of a position of the display image of the three-dimensional dataof the total knee component being adjusted, a position for the totalknee component is calculated as coordinate values of anatomicalcoordinates of a bone where the total knee component is to be placed.

The arthroplasty supporting information calculation system according tothe ninth aspect of the present invention is an arthroplasty supportinginformation calculation system for calculating information that supportsa diagnosis of a patient with knee disordered and total jointreplacement to a total knee component, comprising: an X-ray imagephotographing device (for example, the dedicated cassette base 4 and theX-ray irradiation mechanisms 5 a and 5 b) that photographs an X-rayimage of the patient; a position coordinates acquisition device (forexample, the steel ball grouping (i.e., the frame markers) positiondetection section 12, the camera calibration processing section 13, thepatient bone reference point detection section 14, the patient bonethree-dimensional coordinates acquisition section 15, the sample bonereference point detection section 18, the sample bone three-dimensionalcoordinates acquisition section 19, and the three-dimensional datatransformation processing section 20 of the embodiment) that transformsa configuration of a display image of three-dimensional data of a samplebone such that it matches an X-ray image obtained by photographing bonesof the patient so as to create the approximate three-dimensional data,and, in addition, that determines three-dimensional coordinate values inreal space for this approximate three-dimensional data; and anevaluation parameter calculation device (for example, thethree-dimensional lower limb alignment calculation section 21 of theembodiment) that determines parameters for evaluating positionalrelationships of at least two bones from the approximatethree-dimensional data and from the three-dimensional coordinate valuesof the bones of the patient.

The arthroplasty supporting information calculation system according tothe tenth aspect of the present invention is an arthroplasty supportinginformation calculation system for calculating information that supportsa diagnosis of a patient with knee disordered and total jointreplacement to a total knee component, comprising: an X-ray imagephotographing device that photographs an X-ray image of the patient; aposition coordinates acquisition device (for example, the steel ballgrouping (i.e., the frame markers) position detection section 12, thecamera calibration processing section 13, the patient bone referencepoint detection section 14, the patient bone three-dimensionalcoordinates acquisition section 15, the sample bone reference pointdetection section 18, the sample bone three-dimensional coordinatesacquisition section 19, and the three-dimensional data transformationprocessing section 20 of the embodiment) that transforms a configurationof a display image of three-dimensional data of a sample bone such thatit matches an X-ray image obtained by photographing bones of the patientso as to create the approximate three-dimensional data, and, inaddition, that determines three-dimensional coordinate values in realspace for the approximate three-dimensional data; and a total kneecomponent position calculation device (for example, the total kneecomponent three-dimensional data positioning processing section 23 andthe total knee component position coordinates calculation section 25 ofthe embodiment) that selects a configuration and size of the total kneecomponent for the display image of the approximate three-dimensionaldata, and, by adjusting a position of the display image of thethree-dimensional data of the total knee component, calculates aposition for the total knee component as coordinate values of anatomicalcoordinates of a bone where the total knee component is to be placed.

In the arthroplasty supporting information calculation system accordingto the eleventh aspect of the present invention, in the arthroplastysupporting information calculation system according to the tenth aspect,the X-ray image photographing device photographs X-ray images of bonesof the patient from two directions together with a group of steel balls(for example, the steel balls 6 b of the embodiment) whose respectivethree-dimensional coordinate values in real space are already known.

As a result, in the position coordinates acquisition device, the bonesof the patient are recognized three-dimensionally usingthree-dimensional coordinate values in real space of the group of steelballs and two-dimensional coordinate values taken from two directions ofthe group of steel balls, and the three-dimensional coordinate values ofthe bones of the patient can be accurately determined.

The dedicated cassette base according to the twelfth aspect of thepresent invention is a dedicated cassette base that is used in anarthroplasty supporting information calculation system for calculatinginformation that supports a diagnosis of a patient with knee disorderedand total joint replacement to a total knee component, and that isprovided with: a panel (for example, the panel 6 of the embodiment) thatis held in a direction perpendicular to the bottom surface with one sideof the panel that is in a direction perpendicular to the bottom surfacebeing attached to a central shaft (for example, the central shaft 6 c ofthe embodiment), so that the panel is able to turn from a first positionto a second position around the central shaft while a patient ismaintained in a standing position, and with a recording medium (forexample, the imaging plates (IP) 6 a of the embodiment) forphotographing an X-ray image being provided on two sides of the panel.

As a result, it is possible, without moving the patient that is placedon the cassette base, to rapidly perform X-ray photography from the twodirections that correspond to the first position and the secondposition.

In the dedicated cassette base according to the thirteenth aspect of thepresent invention, in the dedicated cassette base according to thetwelfth aspect of the present invention, at the first position an X-rayimage from a frontal direction of a patient is recorded on the recordingmedium on one surface of the panel, and at the second position an X-rayimage from a direction other than the frontal direction of the patientis recorded on the recording medium on another surface of the panel.

As a result, the labor of replacing the recording medium during X-rayphotography can be omitted and the X-ray photography can be achieved ina short time.

In the dedicated cassette base according to the fourteenth aspect of thepresent invention, in the dedicated cassette base according to thethirteenth aspect of the present invention, the panel is provided with agroup of steel balls (for example, the steel balls 6 b of theembodiment) whose three-dimensional coordinate values in real space areknown.

As a result, it is possible to photograph in an X-ray image a group ofsteel balls that serve as a reference for recognizing the bones of theliving being three-dimensionally together with the bones of the livingbeing.

BRIEF DESCRIPTION THE DRAWINGS

FIG. 1 is a block diagram showing the structure of an arthroplastysupporting information calculation system of an embodiment of thepresent invention.

FIG. 2 is a block diagram showing the structure of an arthroplastysupporting terminal.

FIG. 3 is a view showing the relationship between a group of steel ballsin a three-dimensional space and an image in which these steel balls areprojected onto two-dimensional coordinates.

FIG. 4A is a view showing details of a dedicated cassette base.

FIG. 4B is a view showing details of a dedicated cassette base.

FIG. 5A is a view showing a frame marker of a panel of the dedicatedcassette base.

FIG. 5B is a view showing a frame marker of a panel of the dedicatedcassette base.

FIG. 6 is a flowchart showing a processing sequence of the arthroplastysupporting information calculation system.

FIG. 7A is a view showing an example of the display of a CR image of apatient.

FIG. 7B is a view showing an example of the display of a CR image of apatient.

FIG. 8 is a view showing a portion of a bone for plotting referencepoints of the bone.

FIG. 9 is a view showing a portion of a bone for plotting referencepoints of the bone.

FIG. 10 is a view showing a portion of a bone for plotting referencepoints of the bone.

FIG. 11A is a view for showing anatomical coordinates representing aportion of a bone.

FIG. 11B is a view for showing anatomical coordinates representing aportion of a bone.

FIG. 12A is a view showing a method of determining a cortical bone pointand a diaphysis central point.

FIG. 12B is a view showing a method of determining a cortical bone pointand a diaphysis central point.

FIG. 13 is a view in which three-dimensional data of a sample bone andtotal knee component are displayed three-dimensionally.

FIG. 14 is a view in which a lower limb alignment in approximatethree-dimensional data is shown three-dimensionally by balls andcylinders.

FIG. 15A is a view in which a display image of approximatethree-dimensional data of bone and a display image of three-dimensionaldata of total knee component art superimposed and displayed as a CRimage of a patients bone.

FIG. 15B is a view in which a display image of approximatethree-dimensional data of bone and a display image of three-dimensionaldata of total knee component are superimposed and displayed as a CRimage of a patients bone.

FIG. 16A is a view in which a display image of approximatethree-dimensional data of bone and a display image of three-dimensionaldata of total knee component are superimposed and displayed as a CRimage of a patients bone.

FIG. 16B is a view in which a display image of approximatethree-dimensional data of bone and a display image of three-dimensionaldata of total knee component are superimposed and displayed as a CRimage of a patients bone.

DETAILED DESCRIPTION OF THE INVENTION

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as limited by theforegoing description and is only limited by the scope of the appendedclaims.

A description will now be given of the arthroplasty supportinginformation calculation process and the arthroplasty supportinginformation calculation system of an embodiment of the present inventionwith reference made to the drawings. In the present embodiment, as anexample, a description is given of when information that supports adiagnosis of a patient with knee disordered and total joint replacementto a total knee component is calculated.

The arthroplasty supporting information calculation system of thepresent embodiment is shown in FIG. 1. This system is a system forrealizing an arthroplasty supporting information calculation method, andis provided with an arthroplasty supporting terminal 2 that is used forcalculating information required for the arthroplasty and is operated byan operator 1 (i.e., a doctor), a dedicated cassette base 4 that is usedfor photographing an X-ray image of a patient 3, an X-ray irradiationmechanism 5 a that is used for irradiating X-rays onto the patient froma frontal direction, and an X-ray irradiation mechanism 5 b that is usedfor irradiating X-rays onto the patient 3 from an angle of certaindegrees (ex. 60 degrees). The patient 3 who is positioned on thededicated cassette base 4 stands facing in a predetermined direction.When X-rays are irradiated towards the lower limbs 3 a of the patient 3that are to be operated on from the front and from an angle of 60degrees using the X-ray irradiation mechanisms 5 a and 5 b, X-ray imagesof the patient 3 are recorded on a plurality of imaging plates (IP) 6 athat are mounted on a panel 6. Using the image plates (IP) 6 a asrecording media, X-ray image information is input into the arthroplastysupporting terminal 2 via a digital X-ray system IP reader 7 and isdisplayed on the arthroplasty supporting terminal 2 as a computedradiographic (CR) image.

Note that it is also possible to input X-ray image information directlyinto the arthroplasty supporting terminal 2 from an X-ray sensor otherthan the imaging plates (IP) 6 a.

Furthermore, the X-ray irradiation mechanisms 5 a and 5 b may becombined in a single X-ray irradiation mechanism, provided that thismechanism is able to move rapidly for a short time such as that in whichthe standing posture of the patient does not change.

Next, using the drawings, a description will be given of thearthroplasty supporting terminal 2 that is used in the arthroplastysupporting information calculation system of the present embodiment.FIG. 2 is a block diagram that describes the functional structure of thearthroplasty supporting terminal 2. In FIG. 2, the arthroplastysupporting terminal 2 is provided with an image acquisition interface11, a steel ball grouping (i.e., frame marker) position detectionsection 12, a camera calibration processing section 13, reference pointdetection section 14 for bones of patients, a three-dimensionalcoordinates acquisition section 15 for bones of patients, a database 16for three-dimensional data of sample bones, a three-dimensional dataselection section 17 for sample bones, a reference point detectionsection 18 for sample bones, a three-dimensional coordinates acquisitionsection 19 for sample bones, a three-dimensional data transformationprocessing section 20 for bones, and a three-dimensional lower limbalignment calculation section 21 that are used for calculating athree-dimensional lower limb alignment. Here, the term“three-dimensional data of the sample bone” refers to three-dimensionaldata that represents the configuration of a standard bone of patient andthat is created in advance artificially.

Furthermore, the arthroplasty supporting terminal 2 is provided with anapproximate three-dimensional data database 22, a total knee componentthree-dimensional data positioning processing section 23, a total kneecomponent three-dimensional data database 24, and a total knee componentposition coordinates calculation section 25 that are used forcalculating the position of a total knee component.

The image acquisition interface 11 is an interface that usescommunication to acquire X-ray image information in the form of a CRimage from the digital X-ray system IP reader 7.

In the steel ball grouping (i.e., frame marker) position detectionsection 12, in order to form a CR image for each direction by connectingtogether a plurality of image data, the operator 1 plots five points inan arbitrary sequence from among all the reference cross points(described below in detail) on a CR image, and obtains two-dimensionalcoordinate values of the reference cross points. Furthermore, theoperator 1 plots all the frame marker steel balls 6 b in the respectiveCR images from the front direction and from a direction at an angle of60 degrees to front direction, and obtains two-dimensional coordinatevalues of the steel balls 6 b.

The camera calibration section 13 formulates a projection equation foreach of the front direction CR image and the 60 degree CR image fromtwo-dimensional coordinate values of each of the front direction imageand the 60 degree direction image of the steel balls 6 b and fromthree-dimensional coordinate values of the steel balls 6 b in realspace, and calculates a projection matrix by solving this equation. Notethat English alphabetic characters representing the matrices and vectorsdescribed below, including the character P showing the projectionmatrix, are changed for the bold face characters used in each of theequations.

Specifically, if an explanation is given using FIG. 3, then if (u, v)are taken as the two-dimensional coordinate values in a CR image of thesteel balls 6 b, and if (X, Y, Z) are taken as the three-dimensionalcoordinate values in real space of the steel balls 6 b, the projectionequation is expressed ass{tilde over (m)}=P{tilde over (M)}=A[R,t]{tilde over (M)}  (1)

-   -   wherein    -   s: scalar (numerical)    -   {tilde over (m)}: expansion vector on image plane    -   P: projection matrix    -   {tilde over (M)}: expansion vector in three-dimensional space    -   A: camera internal matrix    -   R: rotation matrix    -   T: translation vector        Here, the projection matrix P is $\begin{matrix}        {P = {\begin{bmatrix}        p_{11} & p_{12} & p_{13} & p_{14} \\        p_{21} & p_{22} & p_{23} & p_{24} \\        p_{31} & p_{32} & p_{33} & p_{34}        \end{bmatrix} = \begin{bmatrix}        p_{1}^{T} & p_{14} \\        p_{2}^{T} & p_{24} \\        p_{3}^{T} & p_{34}        \end{bmatrix}}} & (2)        \end{matrix}$        Accordingly, if Formula (1) is expanded, it is possible to        formulate two linear equations relating to the elements of the        projection matrix P from one three-dimensional point and a        two-dimensional image thereof. $\begin{matrix}        \left\{ \begin{matrix}        {{{p_{1}^{T}M_{i}} - {u_{i}p_{3}^{T}M_{i}} + p_{14} - {u_{i}p_{34}}} = 0} \\        {{{p_{2}^{T}M_{i}} - {v_{i}p_{3}^{T}M_{i}} + p_{24} - {v_{i}p_{34}}} = 0}        \end{matrix} \right. & (3)        \end{matrix}$        Here, if the number of steel balls 6 b is n, the following        equation is obtained        Bp=0  (4)        Note that the following formula shows the elements of the        projection matrix P arranged in a line.        p=[p ₁ ^(T) ,p ₁₄ ,p ₂ ^(T) ,p ₂₄ ,p ₃ ^(T) p ₃₄]^(T)  (5)        While the following formula is a 2n×12 matrix defined from the        two-dimensional coordinate values and the three-dimensional        point of the point B in Formula (3). $\begin{matrix}        {B = \begin{bmatrix}        X_{1} & Y_{1} & Z_{1} & 1 & 0 & 0 & 0 & 0 & {{- u_{1}}X_{1}} & {{- u_{1}}Y_{1}} & {{- u_{1}}Z_{1}} & {- u_{1}} \\        0 & 0 & 0 & 0 & X_{1} & Y_{1} & Z_{1} & 1 & {{- v_{1}}X_{1}} & {{- v_{1}}Y_{1}} & {{- v_{1}}Z_{1}} & {- v_{1}} \\        \vdots & \vdots & \vdots & \vdots & \vdots & \vdots & \vdots & \vdots & \vdots & \vdots & \vdots & \vdots \\        X_{n} & Y_{n} & Z_{n} & 1 & 0 & 0 & 0 & 0 & {{- u_{n}}X_{n}} & {{- u_{n}}Y_{n}} & {{- u_{n}}Z_{n}} & {- u_{n}} \\        0 & 0 & 0 & 0 & X_{n} & Y_{n} & Z_{n} & 1 & {{- v_{n}}X_{n}} & {{- v_{n}}Y_{n}} & {{- v_{n}}Z_{n}} & {- v_{n}}        \end{bmatrix}} & (6)        \end{matrix}$

The camera calibration processing section 13 calculates the projectionmatrix P by solving Formula (4) using an inverse iteration method orNewton's method or the like.

Moreover, in the patient bone reference point detection section 14, inorder to determine three-dimensional coordinate values of characteristicportions of bones from CR images of the patient 3, the operator 1 plotscharacteristic portions (i.e., reference points) of a bone in respectiveCR images from a front direction and a 60 degree direction, and storesthe two-dimensional coordinate values thereof in the patient bonereference point detection section.

The patient bone three-dimensional coordinates acquisition section 15calculates three-dimensional coordinate values in real space ofreference points of bones of the patient 3 using the projection matrix Pcalculated by the camera calibration section 13 from the two-dimensionalcoordinate values of the characteristic portions (i.e., the referencepoints) of the bones of the patient 3. Then, based on thesethree-dimensional coordinate values, sets anatomical coordinates forrepresenting the potions of at least two bones.

The sample bone three-dimensional data database 16 is a database thatstores three-dimensional data of sample bones. In addition, in thesample bone three-dimensional data selection section 17, in order tocalculate a three-dimensional lower limb alignment, the operator 1selects three-dimensional data of at least two sample bones from thesample bone three-dimensional database 16.

In the sample bone reference point detection section 18, in the same wayas in the patient bone reference point detection section 14, in order todetermine three-dimensional coordinate values of characteristic portionsof sample bones, the operator 1 plots characteristic portions (i.e.,reference points) of three-dimensional data of the sample bones inrespective CR images from a front direction and a 60 degree direction,and stores the two-dimensional coordinate values thereof.

In the same way as in the patient bone three-dimensional coordinateacquisition section 15, the sample bone three-dimensional coordinatesacquisition section 19 calculates three-dimensional coordinate values inreal space of reference points of sample bones using the projectionmatrix P calculated by the camera calibration section 13 from thetwo-dimensional coordinate values of the characteristic portions (i.e.,the reference points) of the three-dimensional data of the sample bones.Then, based on these three-dimensional coordinate values, setsanatomical coordinates for representing the potions of at least twobones.

The bone three-dimensional data transformation processing section 20displays a CR image of the bones of the patient 3 superimposed with adisplay image of the three-dimensional data of its Ca data and/or threedimensional data of the sample bones, and determines the relationshipbetween the three dimensional coordinate values in real space of thereference points of the bones of the patient 3 that are determined bythe patient bone three-dimensional coordinates acquisition section 15and the three-dimensional coordinate values in real space of thereference points three-dimensional data of the sample bones that aredetermined by the sample bone three-dimensional acquisition section 19.The bone three-dimensional data transformation processing section 20also automatically transforms the configuration and moves the positionof the display image of the three-dimensional data of the sample bonessuch that the three-dimensional coordinate values of the referencepoints in the three-dimensional data of the sample bones match thereference points of the bones of the patient 3. In addition, the bonethree-dimensional data transformation processing section 20 storesapproximate three-dimensional data of the patient 3 obtained bytransforming the three-dimensional data of the sample bones such that itmatches the reference points of the bones of the patient 3 in theapproximate three-dimensional data database 22.

The three-dimensional lower limb alignment calculation section 21calculates a three-dimensional lower limb alignment from the approximatethree-dimensional data of the patient 3.

The total knee component three-dimensional data positioning processingsection 23 displays a list of optional total knee components in order tocalculate the position of the total knee component. The operator 1selects the desired total knee component three-dimensional data from thetotal knee component three-dimensional data database 24 in which isstored total knee component three-dimensional data. Next, the total kneecomponent three-dimensional data positioning processing section 23displays a display image of the approximate three-dimensional data thatis stored in the approximate three-dimensional data database 22superimposed with a display image of the total knee componentthree-dimensional data. The operator 1 then matches the position of thedisplay image with the position where the total knee component isactually to be placed in the arthroplasty by moving and rotating thedisplay image of the total knee component three-dimensional data, sothat the size of the total knee component and the target position in thearthroplasty are decided.

The total knee component position coordinates calculation section 25calculates the target position in the arthroplasty that has been decidedby the total knee component three dimensional data positioningprocessing section 23 as a target position in anatomical coordinatesdefied using approximate three-dimensional data that is stored in theapproximate three-dimensional data database 22. Note that the targetposition calculated here is the position (i.e., the translationmovement) and the attitude (i.e., the rotation) of the total kneecomponent relative to the anatomical coordinates.

The sample bone three-dimensional data database 16, the approximatethree-dimensional data database 22, and the total knee componentthree-dimensional data database 24 may be formed, for example, so as toinclude a recording medium that can be read from or written to by acomputer such as nonvolatile memory such as a hard disk device, amagneto optical disk device, flash memory or the like, volatile memorysuch as random access memory (RAM), or a combination of these.

Furthermore, the image acquisition interface 11, the steel ball grouping(i.e., the frame marker) position detection section 12, the cameracalibration processing section 13, the patient bone reference pointdetection section 14, the patient bone three-dimensional coordinatesacquisition section 15, the sample bone three-dimensional data selectionsection 17, the sample bone reference point detection section 18, thesample bone three-dimensional coordinates acquisition section 19, thebone three-dimensional data transformation processing section 20, thethree-dimensional lower limb alignment calculation section 21, the totalknee component three-dimensional data positioning processing section 23,and the total knee component position coordinates calculation section 25may each be realized by dedicated hardware. Alternatively, the functionsthereof may be realized by loading a program that is formed by memory ora central processing unit (CPU) in memory and then executing thisprogram.

An input apparatus 2 a and a display apparatus 2 b and the like areconnected to the arthroplasty supporting terminal 2. Here, inputapparatus 2 a refers to an input device such as a keyboard or mouse,while display apparatus 2 b refers to an image display apparatus such asa cathode ray tube (CRT) display device or a liquid crystal displaydevice and to an aural display apparatus such as a speaker.

Next, a description will be given using the drawings of the dedicatedcassette base 4 used in the arthroplasty supporting informationcalculation system of the present embodiment. FIG. 4A and FIG. 4B areviews for describing in further detail the dedicated cassette base 4. InFIG. 4A, the dedicated cassette base 4 is provided with a panel 6 that,when the patient 3 is in a standing position, acquires X-ray images fromtwo directions of the patient 3 in the same attitude. One side in thevertical direction of the panel 6 is attached to a central shaft 6 cthat is vertically mounted on the bottom surface of the dedicatedcassette base 4. As a result, the panel 6 is able to turn withoutcausing the patient 3 to move. An imaging plate (IP) 6 a, which is arecording medium for photographing X-ray images, is provided on both anA surface and a B surface.

As is shown in FIG. 4 b, by rotating the one panel 6 for 240 degrees(=360 degrees −120 degrees), the panel 6 is separated into an A surfacethat records a frontal X-ray image of the patient 3 corresponding to theX-ray irradiation mechanism 5 a, and a B surface that records an X-rayimage from a direction of 60 degrees of the patient 3 corresponding tothe X-ray irradiation mechanism 5 b.

Note that, if an X-ray image of a left lower limb of the patient is tobe acquired an X-ray image in the frontal direction is recorded by the Asurface, while an X-ray image from a direction of 60 degrees is recordedby the B surface. If an X-ray image of a right lower limb is to beacquired, this is reversed.

FIG. 5A, and FIG. 5B are views for describing frame markers embedded inthe panel 6 of the dedicated cassette base 4. Frame markers arereferences used to calculate predicted positions of X-ray irradiationpoints. As is shown in FIG. 5A, there may, for example, be six, shown byA0 to A5, in the A surface of the panel 6, and six, shown by a B0 to B5,in the B surface of the panel 6. As is shown in FIG. 5B, steel balls 6 bare embedded three-dimensionally as reference points in the frontsurface and rear surface of each frame marker.

Furthermore, five steel balls that form reference cross points, whichbecome reference points of each image, are embedded in the A surface andB surface of the panel 6 so that a plurality of X-ray images can beconnected so as to form a single display image.

Note that the three-dimensional coordinate values in real space of thesteel balls 6 b that are embedded in the frame markers, the positions inreal space of the five steel balls that form the reference cross points,the distances between steel balls, and the distances between eachreference cross point are all known.

Next, using the drawings, a description will be given of the processingflow of the arthroplasty supporting information calculation system ofthe present embodiment using as an example a case in which informationis calculated that supports an operation to replace a patient knee jointwith a total knee component.

FIG. 6 is a flowchart describing the processing flow of an arthroplastysupporting information calculation system. When the operator 1 performsthe arthroplasty to read CR image data from both a frontal direction and60 degree direction of a subject patient 3 from the digital X-ray systemIP reader 7, the arthroplasty supporting terminal 2 acquires the CRimage data via the image acquisition interface 11 and displays it on ascreen of the display apparatus 2 b (step S1).

It is also possible to read CR image data directly from an X-ray sensorand display it on the screen of the display apparatus 2 b without goingthrough the digital X-ray system IP reader 7.

Next, when the operator 1 plots all of the reference cross points on theCR image, the steel ball grouping (i.e., the frame markers) positiondetection section 12 stores two-dimensional coordinate values of all ofthe plotted reference cross points. Then, based on these two-dimensionalcoordinate values, positional relationships of the reference crosspoints are automatically determined and are stored in a predeterminedorder (step S2).

When the plotting of the reference cross points is completed and theoperator 1 has plotted all of the frame marker steel balls 6 b of the CRimage, the steel ball grouping (i.e., the frame markers) positiondetection section 12 stores two-dimensional coordinate values of all ofthe plotted steel balls 6 b, and determines relationships between thethree-dimensional coordinate values in real space of the steel balls 6 band the two-dimensional coordinate values on the CR images in thefrontal direction and the 60 degree direction (step S3).

Note that using characteristic information such as the brightness andconfiguration of the steel balls 6 b, the steel balls 6 b may also bedetected from the CR images automatically.

FIG. 7A and FIG. 7B are examples of displays of CR images. FIG. 7A is aCR image representing an X-ray image from the frontal direction of thepatient 3, while FIG. 7B is a CR image representing an X-ray image froma 60 degree direction of the patient 3. In these drawings, with thereference cross points in the A surface of the panel 6 taken as XA1 toXA3 and the reference cross points in the B surface of the panel 6 takenas XB1 to XB3, the CR images from the respective directions arereproduced. In addition, with the frame markers in the A surface of thepanel 6 taken as A1 to A5 and the frame markers in the B surface of thepanel 6 taken as B1 to B5, the CR images from the respective directionsare reproduced. Note that the other symbols shown and FIG. 7 aredescribed below in detail.

Once the two-dimensional coordinate values of the CR image from thefrontal direction and the CR image from the 60 degree direction of theframe marker steel balls 6 b as well as the three-dimensional coordinatevalues in real space thereof have been determined, the cameracalibration processing section 13 formulates a projection equation, asdescribed above, from the relationships between the two-dimensionalcoordinate values and the three-dimensional coordinate values of therespective directions, and calculates the projection matrix P by solvingthis equation (step S4).

Note that if the positional relationships of the X-ray irradiationmechanisms 5 a and 5 b and the dedicated cassette base 4 are fixed andknown, then because it is possible to calculate and store the projectionmatrix P in advance, step S2 to step S4 may be omitted.

Next, once the operator 1 has plotted characteristic portions (i.e.,reference points) of the bones of the patient 3 in respective CR imagesfrom both a frontal direction and from a 60 degree direction in order todetermine three-dimensional coordinate values of the characteristicportions of the bones from the CR images of the patient 3, the patientbone reference point detection section 14 stores all two-dimensionalcoordinate values of the plotted reference points (step S5).

This operation will be described in detail using FIG. 8 through FIG. 10.FIG. 8 through FIG. 10 are views showing portions that are plotted asbone reference points. The respective reference points are plotted as isdescribed below.

-   (1) Femoral head reference point (see FIG. 8)

In order to determine a central point obtained by making an approximatecircle of the outline of the bone head of the femur 50, the operator 1plots three femoral head reference points 52. The patient bone referencepoint detection section 14 then approximates the bone head configurationas a femoral head approximate circle 53 from two-dimensional coordinatevalues of the (three) femoral head reference points 52, and calculatesthe two-dimensional coordinate values of the femoral head central point54.

-   (2) Reference point of epicondylus mediale (see FIG. 9)

The operator 1 plots three reference points of medial condyle 56 inorder to determine a central point that is obtained by making anapproximate circle of the outline of the epicondylus mediale 55. Thepatient bone reference point detection section 14 then approximates theepicondylus mediale 55 as an epicondylus mediale approximate circle 57from two-dimensional coordinate values of the (three) reference pointsof medial condyle 56, and calculates the two-dimensional coordinatevalues of a center point of medial condyle 58.

-   (3) Reference point of lateral condyle (see FIG. 9)

The operator 1 plots three reference points of lateral condyle 60 inorder to determine a central point that is obtained by making anapproximate circle of the outline of the lateral condyle 59. The patientbone reference point detection section 14 then approximates the lateralcondyle 59 as an lateral condyle approximate circle 61 fromtwo-dimensional coordinate values of the (three) reference points oflateral condyle 60, and calculates the two-dimensional coordinate valuesof a center point of lateral condyle 62.

-   (4) Tibia proximal joint surface inner edge point (see FIG. 9)

The operator 1 plots a tibia proximal joint surface inner edge point 71,and the patient bone reference point detection section 14 stores thetwo-dimensional coordinate values thereof.

-   (5) Tibia proximal joint surface outer edge point (see FIG. 9)

The operator 1 plots a tibia proximal joint surface outer edge point 72,and the patient bone reference point detection section 14 stores thetwo-dimensional coordinate values thereof.

-   (6) Tibia distal joint surface inner edge point (see FIG. 10)

The operator 1 plots a tibia distal joint surface inner edge point 74,and the patient bone reference point detection section 14 stores thetwo-dimensional coordinate values thereof.

-   (7) Tibia distal joint surface outer edge point (see FIG. 10)

The operator 1 plots a tibia distal joint surface outer edge point 75,and the patient bone reference point detection section 14 stores thetwo-dimensional coordinate values thereof.

-   (8) Apex of fibular head (see FIG. 9)

The operator 1 plots an apex of fibular head 81, and the patient bonereference point detection section 14 stores the two-dimensionalcoordinate values thereof.

-   (9) Distal end of fibula (see FIG. 10)

The operator 1 plots a distal end of fibula 82, and the patient bonereference point detection section 14 stores the two-dimensionalcoordinate values thereof.

In the patient bone reference detection section 14, characteristicreference points of the bones are plotted on the frontal direction CRimage and the 60 degree direction CR image, and once the two-dimensionalcoordinate values thereof have been obtained, the patient bonethree-dimensional coordinate acquisition section 15 calculatesthree-dimensional coordinate values in real space that correspond to thetwo-dimensional coordinate values of the reference points of the bonesusing the projection matrix P determined by the camera calibrationprocessing section 13 in step S4 (step S6).

Specifically, firstly, when the three-dimensional coordinate values ofthe reference points are: $\begin{matrix}{{{projection}\quad{matrix}\quad P_{f}\quad{in}\quad{frontal}\quad{direction}} = {\quad\begin{bmatrix}p_{f_{11}} & p_{f_{12}} & p_{f_{13}} & p_{f_{14}} \\p_{f_{21}} & p_{f_{22}} & p_{f_{23}} & p_{f_{24}} \\p_{f_{31}} & p_{f_{32}} & p_{f_{33}} & p_{f_{34}}\end{bmatrix}}} & \left( {7\text{-}1} \right) \\{{{projection}\quad{matrix}\quad P_{q}\quad{in}\quad 60\quad{degree}\quad{direction}} = {\quad\begin{bmatrix}p_{q_{11}} & p_{q_{12}} & p_{q_{13}} & p_{q_{14}} \\p_{q_{21}} & p_{q_{22}} & p_{q_{23}} & p_{q_{24}} \\p_{q_{31}} & p_{q_{32}} & p_{q_{33}} & p_{q_{34}}\end{bmatrix}}} & \left( {7\text{-}2} \right)\end{matrix}$and the three-dimensional coordinate values being determined are (X, Y,Z), then if

-   -   (u_(f), v_(f)): plotted two-dimensional coordinate values on        frontal direction CR image    -   (u_(q), v_(q)) plotted two-dimensional coordinate values on 60        degree direction CR image $\begin{matrix}        {B = \begin{bmatrix}        u_{f} & {p_{f_{31}} - p_{f_{11}}} & u_{f} & {p_{f_{32}} - p_{f_{12}}} & u_{f} & {p_{f_{33}} - p_{f_{13}}} \\        v_{f} & {p_{f_{31}} - p_{f_{21}}} & v_{f} & {p_{f_{32}} - p_{f_{22}}} & v_{f} & {p_{f_{33}} - p_{f_{23}}} \\        u_{q} & {p_{q31} - p_{q11}} & u_{q} & {p_{q32} - p_{q12}} & u_{q} & {p_{q33} - p_{q13}} \\        v_{q} & {p_{q31} - p_{q21}} & v_{q} & {p_{q32} - p_{q22}} & v_{q} & {p_{q33} - p_{q23}}        \end{bmatrix}} & \left( {8\text{-}1} \right) \\        {b = \begin{bmatrix}        {p_{f_{14}} - u_{f}} & p_{f_{34}} \\        {p_{f_{24}} - v_{f}} & p_{f_{34}} \\        {p_{q14} - u_{q}} & p_{q34} \\        {p_{q24} - v_{q}} & p_{q34}        \end{bmatrix}} & \left( {8\text{-}2} \right)        \end{matrix}$        then the three-dimensional coordinate values in real space are        determined by: $\begin{matrix}        {\begin{pmatrix}        X \\        Y \\        Z        \end{pmatrix} = {{\left( {B^{T}B} \right)^{- 1} \cdot B^{T}}{b\quad\left( \begin{matrix}        {B^{T}\text{:}\quad{transposed}\quad{matrix}\quad{of}\quad{matrix}\quad B} \\        {{()}^{- 1}\text{:}\quad{inverse}\quad{matrix}\quad{of}\quad{contents}\quad{of}\quad{brackets}}        \end{matrix} \right.}}} & (9)        \end{matrix}$

Next, based on the determine three-dimensional coordinate values, twoanatomical coordinates are set on the femur 50 side and the tibia 70 andfibula 80 side (step S7).

Specifically, if the two anatomical coordinates are described withreference made to FIG. 8 through FIG. 10 and to FIG. 11A and FIG. 11Bthat show anatomical coordinates, then they are set in the mannerdescribed below.

-   1. Anatomical coordinates on the femur 50 side origin; central point    between the center point of medial condyle 58 and the center point    of lateral condyle 62.-   X axis: segment 63 connecting the center point of medial condyle 58    and the center point of lateral condyle 62.-   Y axis: segment from the origin to the femoral head central point 54    that is perpendicular to X axis and segment 64 (i.e., Z′ axis).-   Z axis: segment perpendicular to X axis and Y axis. The orientation    of the vector determined by the vector product (i.e., the X axis×the    Y axis) is positive,-   2. Anatomical coordinates on the tibia 70 and fibula 80 side origin:    central point between the tibia proximal joint surface inner edge    point 71 and the tibia proximal joint surface outer edge point 72.-   Z axis; segment 77 connecting the origin and the central point    between the tibia distal joint surface inner edge point 74 and the    tibia distal joint surface outer edge point 75. The orientation from    the origin to the central point between the tibia distal joint    surface inner edge point 74 and the tibia distal joint surface outer    edge point 75 is negative.-   X axis: vertical line from the Z axis that passes through the origin    and that is the segment that intersects the segment 83 connecting    the apex of fibular head 81 with the distal end of fibula 82. The    leftward orientation heading from the X-ray irradiation mechanism is    positive.-   Y axis: segment perpendicular to X axis and Z axis. The orientation    of the vector determined by the vector product (i.e., the Z axis×the    X axis) is positive.

When the anatomical coordinates are set, because the operator 1 plotsthe bone cortex points on a CR image, the patient bone reference pointdetection section 14 calculates the two-dimensional coordinate values ofthe diaphysis central point (i.e., the central point between two bonecortex points) from the two-dimensional values of the bone cortex points(step S8).

Specifically, the patient bone reference point detection section 14divides into ten segments the lengths of the femur 50, the tibia 70, andthe fibula 80 (i.e., the distances from a minus end point to a plus endpoint on the Z axis on the anatomical coordinates of each one) using thesegment that intersects with the Z axis, and projects those segments ina frontal direction and a 60 degree direction so as to display them onthe screen of the display apparatus 2 b. The operator 1 then plotsintersection points between the bone cortex points of each bone and theten segment dividing lines of the diaphysis sections in the frontal CRimages and the 60 degree CR images. As a result, the two-dimensionalcoordinate values of the bone cortex points are calculated.

FIG. 12A and FIG. 12B are views showing a method of determining adiaphysis point and a bone cortex central point and take as thediaphysis points 92 intersection points between diaphysis points of abone (for example, the femur 50) and the ten segment dividing lines 91that are projected in a frontal CR image and a 60 degree CR image. Thediaphysis section is the section that is sandwiched by the fourth andninth segment dividing lines 91 (going from the top), and the diaphysiscentral point 93 is the central point of the two bone cortex points 92within this section.

Once the two-dimensional coordinate values of the diaphysis centralpoint 93 has been calculated using the patient bone reference pointdetection section 14, the patient bone three-dimensional coordinateacquisition section 15, in the same way as in the case of the bonereference points in step S6, calculates three-dimensional coordinatevalues in real space that correspond to the two-dimensional coordinatevalues of the diaphysis central point 93 using the projection matrix Pdetermined by the camera calibration processing section 13 in step S4(step S9).

The operator 1 then selects sample bone three-dimensional data of thefemur 50, the tibia 70, and the fibula 80, which form the source forcreating approximate three-dimensional data of the bones of the patient3 from among lists in the sample bone three-dimensional data database 16displayed on the display apparatus 2 b. When the three-dimensional dataof the sample bone is selected, the sample bone three-dimensional dataselection section 17 acquires three-dimensional data of the relevantsample bone from the sample bone three-dimensional data database 16(step S10).

When the sample bone three-dimensional data selected by the operator 1has been acquired, the operator 1 plots reference points of thethree-dimensional data of the sample bone from a frontal direction andfrom a 90 degree direction using the same procedure as was used in stepS5. Here, the reason why the reference points are plotted from a 90degree direction and not a 60 degree direction is in order to obtainmore accurate reference coordinates. When the operator 1 has plotted thereference points, the sample bone reference point detection section 18stores all the two-dimensional coordinate values of the plottedreference points (step S11).

Next, using the same procedure as was used in step S6, the sample bonethree-dimensional coordinates acquisition section 19 calculatesthree-dimensional coordinate values in real space that correspond to thetwo-dimensional coordinate values of the reference points of the boneusing the projection matrix P determined by the camera calibrationprocessing section 13 in step S4 (step S12).

Furthermore, based on the determined three-dimensional coordinatevalues, using the same procedure as was used in step S7, two anatomicalcoordinates are set, one for the tibia and fibula side and one for thefemur side of the sample bone three-dimensional data (step S13).

Note that the processing from step S11 to step S13 is performed inadvance when preparing sample bone three-dimensional data and does notneed to be executed each time provided that the information thereof hasbeen recorded.

Once the reference points in the CR image of the bone of the patient 3and the reference points of the sample bone three-dimensional data havebeen determined, sample bone positioning processing (step S14) isperformed in the bone three-dimensional data transformation processingsection 20 such that the reference points in the CR image of the bone ofthe patient 3 match the reference points of the sample bonethree-dimensional data.

Specifically, in the first positioning processing, firstly, arelationship between reference points in the CR image of the bone of thepatient 3 and reference points of the sample bone three-dimensional datais determined. Next, as was previously shown in FIG. 7A and FIG. 7B, aCR image of the bone of the patient 3 and a two-dimensional projectedimage of the sample bone three-dimensional data are simultaneouslydisplayed on the display apparatus 2 b. Next, the two-dimensionalprojected image 100 of the sample bone three-dimensional data that isdisplayed on the CR image of the bone of the patient 3 on the displayapparatus 2 b is converted using translation movement, rotation, scaleconversion and the like such that three-dimensional coordinate values ofcorresponding reference points match each other. Here, the translationmovement and rotation are performed by a general matrix operation, andthe scale conversion processing is performed using a warping process orthe like.

As a result of this processing, the reference points of the sample boneoverlap with the reference points of the bone of the patient 3, and theposition, attitude, and size of the bone is summarily determined.

Next, in the second positioning processing, as is shown in FIG. 12A andFIG. 12B, the lengths of the femur 50, tibia 70, and fibula 80 (i.e.,the distances from a minus end point to a plus end point on the Z axison the anatomical coordinates of each one) are divided into ten segmentsusing the segment that intersects with the Z axis, and these segmentsare projected in a frontal direction and a 60 degree direction and aredisplayed on the screen of the display apparatus 2 b. The operator 1then performs movement, rotation, expansion, and contraction processingsuch that slice cross-sections of the sample bone at each of the tensegment dividing lines 91 match the slice cross-sections of the bone ofthe patient 3 in the CR image.

The symbol 100A in FIG. 13 is a view showing three-dimensionally thethree-dimensional data of the sample bone. The bone three-dimensionaldata transformation processing section 20 appropriately executesmovement, rotation, expansion, and contraction processing such that theslice cross-sections of the display image of the sample bonethree-dimensional data that is projected and displayed on the CRP imageof the bone of the patient 3 matches the outline of the bone of thepatient 3 on this CR image. Note that the symbol 110A shown in FIG. 13is described below.

Once the slice cross-sections of the display image of the sample bonethree-dimensional data match the slice cross-sections of the bone of thepatient 3 in the CR image at all positions of the ten segment dividinglines 91, interpolation processing is performed on the three-dimensionaldata between the ten segment dividing lines 91.

Note that, as a result of this processing, the sample bone matches thebone of the patient 3, and forms approximate three-dimensional data thatcorresponds to the patient 3.

The bone three-dimensional data transformation processing section 20stores this approximate three-dimensional data in the approximatethree-dimensional data database 22 (step S15). FIG. 14 is a view inwhich a lower limb alignment in an approximate three-dimensional datadisplay image is shown three-dimensionally by balls and cylinders. Here,in FIG. 14, lower limb alignments in which “A” has been added onto thesymbol numbers show that they are a three-dimensional display of lowerlimb alignments having symbols represented by only the same symbols thatare shown in FIG. 11.

Next, in order to perform a diagnosis of joint disorders of the patient3, the three-dimensional lower limb alignment calculation section 21calculates, for example, the 11 types of lower limb alignment evaluationparameters given below from the approximate three-dimensional data inwhich the aforementioned lower limb alignments are three-dimensionallydisplayed by balls and cylinders (step S16).

The 11 items are (1) degree of femur curvature, (2) position of maximumfemur curvature, (3) degree of tibia curvature, (4) position of maximumtibia curvature, (5) femur bone angle, (6) knee joint extension angle,(7) lower limb load line transit point, (8) knee joint fissure angle,(9) femur angle of anteversion, (10) knee joint angle of torsion, and(11) tibia twist angle. The three-dimensional lower limb alignmentcalculation section 21 displays numerical values for the calculatedthree-dimensional lower limb alignments on the display apparatus 2 b.

In contrast, in order to create a preplan for when the operation toreplace the knee joint of the patient 3 with a total knee component isperformed, the operator 1 selects total knee component of an optionalsize from a list that is displayed on the screen of the displayapparatus 2 b. The total knee component three-dimensional datapositioning processing section 23 acquires approximate three-dimensionaldata of the bones of the patient 3 from the approximatethree-dimensional data database 22, and also acquires total kneecomponent three-dimensional data selected from the total knee componentthree-dimensional data database 24 (step S17).

Next, as is shown in FIG. 15A and FIG. 15B, a display image 101 of theapproximate three-dimensional data of the patient 3 that is stored inthe approximate three-dimensional data database 22 is displayed on thedisplay apparatus 2 b simultaneously with the total knee component image110. The operator 1 then performs translation movement and rotation onthe image 110 of the total knee component that are displayed on thedisplay image 101 of the approximate three-dimensional data of the boneon the display apparatus 2 b, so as to position of the image 110 suchthat the total knee component match the positions where they are to beactually placed in the operation.

Here, if necessary, the operator 1 may repeat the selection of thethree-dimensional data total knee component and the position matchingthereof on the CR image until the a knee joint of a size that may bethought most suitable for the patient 3 is found. Based on the resultsof this, the total knee component three-dimensional data positioningprocessing section 23 stores the size of the components of the totalknee component that is used (step S18). Furthermore, once the size ofthe components of the total knee component have been decided, as isshown in FIG. 16A and FIG. 16B, the operator 1 matches accurate targetpositions of the total knee component. Note that, in FIG. 13, which wasshown previously, the image 110 of the total knee component is shown ina three-dimensional view (i.e., the symbol 110A).

When the size of the total knee component and accurate target positionshave been decided by the total knee component three-dimensional datapositioning processing section 23, the total knee component positioncoordinates calculation section 25 calculates target positions of thetotal knee component in anatomical coordinates of the femur and/or tibiathat are defined by approximate three-dimensional data (step S19). Notethat the term “target position” used here refers to the position (i.e.,the translation movement) and the attitude (i.e., the rotation) of thetotal knee component relative to the anatomical coordinates.

Note also that, in the above described embodiment, a description isgiven of an example in which the arthroplasty supporting informationcalculation system is used when diagnosis of the patient and, inparticular, the knee joint thereof, and the operation to replace thiswith the total knee component are performed. However, provided that itis possible to acquire X-ray images photographed from two directions,this system may be used not only for the patient and, moreover, for kneejoint, but, starting with hip joint, for diagnoses of joints of anyportion of all types of living bodies that have a skeleton, and foroperations to replace these joints with artificial components.

Moreover, in the above described embodiment, when creating a CR imagefrom an X-ray image of a bone of the patient 3, the arthroplastysupporting information calculation system extracts an outline of thebone (bone outline extraction processing) and emphasizes this outline(outline emphasizing processing). As a result, the CR image may beprocessed so as to be even more easily viewed by the operator 1.Moreover, the transformation operation is unnecessary whenthree-dimensional data of the bones of the actual patient are obtainedby CT scan or the like.

It is also possible to perform information calculation processing thatsupports a diagnosis of joint disorders or an operation of the joint byrecording a program that realizes the functions of the arthroplastysupporting terminal 2 in the above described embodiment on a computerreadable recording medium, and then by reading and executing the programrecorded on this recording medium using a computer system. Note that theterm “computer system” used here includes OS and hardware such asperipheral devices. Moreover, if a WWW system is being used, the term“computer system” also includes homepage providing environments (ordisplay environments). The term “computer readable recording medium”refers to transportable media such as flexible disks, magneto opticdisks, ROM, CD-ROM and the like and to recording devices such as harddisks that are incorporated in a computer system. Furthermore, the term“computer readable recording medium” may also refer to computers thatform servers and clients when the program is transmitted via acommunication circuit such as a telephone line or a network such as theInternet.

The arthroplasty supporting information calculation system of thepresent embodiment photographs a patient 3 using X-rays from twodirections using the dedicated cassette base 4, determines a projectionmatrix P of a CR image and of real space using frame markers whosethree-dimensional coordinate values that appear on a CR image createdfrom this X-ray image are known, and recognizes lower limbs 3 a of apatient 3 that are to be operated on three-dimensionally usingthree-dimensional coordinate values. Then, by transforming a displayimage of three-dimensional data of sample bones to match the CR image ofthe patient 3, approximate three-dimensional data of the patient 3 iscreated. Evaluation parameters for evaluating positional relationshipsbetween a femur, and a tibia and fibula are then calculated fromthree-dimensional coordinate values determined from this approximatethree-dimensional data of the bones.

Accordingly, because it is possible to photograph a patient in astanding position using the dedicated cassette base 4, the effect isobtained that it is possible to acquire an X-ray image in a state inwhich a load is actually applied to the knee joint due to this standingstate, without placing any burden on the patient.

Moreover, by three-dimensionally recognizing the knee joint of thepatient using X-ray images from two directions, in comparison with whena three-dimensional image is acquired by CT scan, the effect is obtainedthat the patient is only exposed to a small amount of radiation.

Furthermore, the conventional problem that the lower limb alignment(i.e., the positional relationship between the femur and tibia), whichis three-dimensional, was determined using X-ray photographs from twodirections, which are two-dimensional images, is solved and it ispossible to three-dimensionally recognize and diagnose the bone andjoint.

Moreover, as a result of the operator 1 adjusting the position of adisplay image of three-dimensional data of the total knee component tomatch a display image of approximate three-dimensional data of a bone ofthe patient 3 based on determined three-dimensional coordinate values,the position of a total knee component is calculated as anatomicalcoordinate values that represent the positions of at least to bones.Accordingly, by using information calculated using the arthroplastysupporting information calculation system of the present embodiment in apreoperative task such as selecting the total knee component anddeciding the position, which have hitherto depended a great deal on theexperience of the doctor, it is possible to increase stability inoperation results, improve safety, and improve reproducibility in theplacement of the total knee component in the target position and thelike.

Furthermore, as a result of the doctor and patient simultaneouslyconfirming information that supports the above described diagnosis andoperation, which is displayed on the arthroplasty supporting terminal 2,the arthroplasty supporting information calculation system can be usedas an informed consent tool for deepening the understanding and sense ofsecurity of the patient towards the diagnosis and operation.

1. An arthroplasty supporting information calculation method forcalculating information that supports a diagnosis of a patient with kneedisordered and total joint replacement to a total knee component,comprising: position coordinates acquisition processing in which aconfiguration of a display image of three-dimensional data of a samplebone is transformed so as to match an X-ray image obtained byphotographing bones of a patient so as to create three-dimensional datathat is approximate to the bones of the patient, and, in addition, inwhich three-dimensional coordinate values in real space are determinedfor the three-dimensional data that is approximate to these bones of thepatient; and evaluation parameter calculation processing in whichpositional relationships of at least two bones are evaluated from thethree-dimensional data that is approximate to the bones of the patientand from the three-dimensional coordinate values of the bones of thepatient.
 2. An arthroplasty supporting information calculation methodfor calculating information that supports a diagnosis of a diagnosis ofa patient with knee disordered and total joint replacement to a totalknee component, comprising: position coordinates acquisition processingin which a configuration of a display image of three-dimensional data ofa sample bone is transformed so as to match an X-ray image obtained byphotographing bones of a patient so as to create three-dimensional datathat is approximate to the bones of the patient, and, in addition, inwhich three-dimensional coordinate values in real space are determinedfor the three-dimensional data that is approximate to these bones of thepatient; and total knee component position calculation processing inwhich a configuration and size of the total knee component is selectedfor the display image of the three-dimensional data that is approximateto the bones of the patient, and, as a result of a position of thedisplay image of the three-dimensional data of the total knee componentbeing adjusted, a position for the total knee component is calculated ascoordinate values of anatomical coordinates of a bone where the totalknee component is to be placed.
 3. The arthroplasty supportinginformation calculation method according to claim 1, wherein theposition coordinates acquisition processing derives a projection matrixthat represents a projection relationship between real space andtwo-dimensional planes of projection coming from two directions fromthree-dimensional coordinate values of a group of steel balls whosethree-dimensional coordinate values in real space are known andtwo-dimensional coordinate values of the group of steel balls thatappears in X-ray images that are obtained by photographing the bones ofthe patient from two directions, and, using this projection matrix,determines three-dimensional coordinate values of the approximatethree-dimensional data of the bones of the patient.
 4. The arthroplastysupporting information calculation method according to claim 2, whereinthe position coordinates acquisition processing derives a projectionmatrix that represents a projection relationship between real space andtwo-dimensional planes of projection coming from two directions fromthree-dimensional coordinate values of a group of steel balls whosethree-dimensional coordinate values in real space are known andtwo-dimensional coordinate values of the group of steel balls thatappears in X-ray images that are obtained by photographing the bones ofthe patient from two directions, and, using this projection matrix,determines three-dimensional coordinate values of the approximatethree-dimensional data of the bones of the patient.
 5. The arthroplastysupporting information calculation method according to claim 3, whereinthe arthroplasty supporting information calculation method includesreference point acquisition processing in which points that showcharacteristics of bones that can be observed from both of twodirections are plotted on two-dimensional images that are taken from thetwo directions in which are displayed bones of the patient or bones thatapproximate a configuration of bones of the patient, and referencepoints that show characteristics and structures of the bones aredetermined from the plotted points that show the characteristics of thebones, and the position coordinate acquisition processing determinesthree-dimensional coordinate values of the approximate three-dimensionaldata of the bones of the patient by calculating three dimensionalcoordinate values in real space from the reference points using theprojection matrix.
 6. The arthroplasty supporting informationcalculation method according to claim 4, wherein the arthroplastysupporting information calculation method includes reference pointacquisition processing in which points that show characteristics ofbones that can be observed from both of two directions are plotted ontwo-dimensional images that are taken from the two directions in whichare displayed bones of the patient or bones that approximate aconfiguration of bones of the patient, and reference points that showcharacteristics and structures of the bones are determined from theplotted points that show the characteristics of the bones, and theposition coordinate acquisition processing determines three dimensionalcoordinate values of the approximate three-dimensional data of the bonesof the patient by calculating three-dimensional coordinate values inreal space from the reference points using the projection matrix.
 7. Thearthroplasty supporting information calculation method according toclaim 5, wherein the reference point acquisition processing determinesthe reference points by approximating a surface configuration of a bonefrom plotted points that show characteristics of the bone.
 8. Thearthroplasty supporting information calculation method according toclaim 6, wherein the reference point acquisition processing determinesthe reference points by approximating a surface configuration of a bonefrom plotted points that show characteristics of the bone.
 9. Thearthroplasty supporting information calculation method according toclaim 1, wherein the arthroplasty supporting information calculationmethod includes reference point acquisition processing in which pointsthat show characteristics of bones that can be observed from both of twodirections are plotted on two-dimensional images that are taken from thetwo directions in which are displayed bones of the patient or bones thatapproximate a configuration of bones of the patient, and referencepoints that show structures of the bones are determined as a result of asurface configuration of the bones being approximated from the plottedpoints that show the characteristics of the bones, and the evaluationparameter calculation processing determines the parameters using thesereference points.
 10. An arthroplasty supporting information calculationprogram for calculating information that supports a diagnosis of apatient with knee disordered and total joint replacement to a total kneecomponent, that executes on a computer: position coordinates acquisitionprocessing in which a configuration of a display image ofthree-dimensional data of a sample bone is transformed so as to match anX-ray image obtained by photographing bones of a patient so as to createthree-dimensional data that is approximate to the bones of the patient,and, in addition, in which three-dimensional coordinate values in realspace are determined for the three-dimensional data that is approximateto these bones of the patient; and evaluation parameter calculationprocessing in which positional relationships of at least two bones areevaluated from the three-dimensional data that is approximate to thebones of the patient and from the three-dimensional coordinate values ofthe bones of the patient.
 11. An arthroplasty supporting informationcalculation program for calculating information that supports adiagnosis of a patient with knee disordered and total joint replacementto a total knee component, that executes on a computer: positioncoordinates acquisition processing in which a configuration of a displayimage of three-dimensional data of a sample bone is transformed so as tomatch an X-ray image obtained by photographing bones of a patient so asto create three-dimensional data that is approximate to the bones of thepatient, and, in addition, in which three-dimensional coordinate valuesin real space are determined for the three-dimensional data that isapproximate to these bones of the patient; and total knee componentposition calculation processing in which a configuration and size of thetotal knee component is selected for the display image of thethree-dimensional data that is approximate to the bones of the patient,and, as a result of a position of the display image of thethree-dimensional data of the total knee component being adjusted, aposition for the total knee component is calculated as coordinate valuesof anatomical coordinates of a bone where the total knee component is tobe placed.
 12. An arthroplasty supporting information calculation systemfor calculating information that supports a diagnosis of a patient withknee disordered and total joint replacement to a total knee component,comprising: an X-ray image photographing device that photographs anX-ray image of a patient; a position coordinates acquisition device thattransforms a configuration of a display image of three-dimensional dataof a sample bone such that it matches an X-ray image obtained byphotographing bones of a patient so as to create three-dimensional datathat is approximate to the bones of the patient, and, in addition, thatdetermines three-dimensional coordinate values in real space for thethree-dimensional data that is approximate to these bones of thepatient; and an evaluation parameter calculation device that determinesparameters for evaluating positional relationships of at least two bonesfrom the three-dimensional data that is approximate to the bones of thepatient and from the three-dimensional coordinate values of the bones ofthe patient.
 13. An arthroplasty supporting information calculationsystem for calculating information that supports a diagnosis of apatient with knee disordered and total joint replacement to a total kneecomponent, comprising: an X-ray image photographing device thatphotographs an X-ray image of a patient; a position coordinatesacquisition device that transforms a configuration of a display image ofthree-dimensional data of a sample bone such that it matches an X-rayimage obtained by photographing bones of a patient so as to createthree-dimensional data that is approximate to the bones of the patient,and, in addition, that determines three-dimensional coordinate values inreal space for the three-dimensional data that is approximate to thesebones of the patient; and a total knee component position calculationdevice that selects a configuration and size of the total knee componentfor the display image of the three-dimensional data that is approximateto the bones of the patient, and, by adjusting a position of the displayimage of the three-dimensional data of the total knee component,calculates a position for the total knee component as coordinate valuesof anatomical coordinates of a bone where the total knee component is tobe placed.
 14. The arthroplasty supporting information calculationsystem according to claim 12, wherein the X-ray image photographingdevice photographs X-ray images of bones of the patient from twodirections together with a group of steel balls whose respectivethree-dimensional coordinate values in real space are already known. 15.The arthroplasty supporting information calculation system according toclaim 13, wherein the X-ray image photographing device photographs X-rayimages of bones of the patient from two directions together with a groupof steel balls whose respective three-dimensional coordinate values inreal space are already known.
 16. A dedicated cassette base that is usedin an arthroplasty supporting information calculation system forcalculating information that supports a diagnosis of a patient with kneedisordered and total joint replacement to a total knee component, andthat is provided with: a panel that is held in a direction perpendicularto the bottom surface with one side of the panel that is in a directionperpendicular to the bottom surface being attached to a central shaft,so that the panel is able to turn from a first position to a secondposition around the central shaft while a patient is maintained in astanding position, and with a recording medium for photographing anX-ray image being provided on two sides of the panel.
 17. The dedicatedcassette base according to claim 16, wherein at the first position anX-ray image from a frontal direction of the patient is recorded on therecording medium on one surface of the panel, and at the second positionan X-ray image from a direction other than the frontal direction of thepatient is recorded on the recording medium on another surface of thepanel.
 18. The dedicated cassette base according to claim 16, whereinthe panel is provided with a group of steel balls whosethree-dimensional coordinate values in real space are known.
 19. Thededicated cassette base according to claim 17, wherein the panel isprovided with a group of steel balls whose three-dimensional coordinatevalues in real space are known.